Yeah
Part of speech: adverb
Definition: yes
Part of speech: interjection
Definition: Expressing joy, celebration, glee, etc.
Example sentence: I get asked a lot about being a woman within the industry and how difficult it is, and yeah, it is - but it's difficult for everybody... I'm not a 'burn-your-bra' feminist.
Yea
Part of speech: interjection
Definition: yeah, right, yes(in some dialects of American English, including Southern, Western, and African American Vernacular) Yeah, right, yes.
Part of speech: adverb
Definition: yesThus, so (now often accompanied by a hand gesture)
Part of speech: noun
Definition: An affirmative vote, usually but not always spoken